Semi-crystalline polymers are useful as engineering thermoplastics because they possess advantageous chemical, physical, and electrical properties, and because they can be readily processed by thermal means. For example, linear semi-crystalline polymers such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) are processed by injection molding and extrusion in the manufacture of plastic components.
It is important that semi-crystalline polymers be heat resistant, because they are typically processed at high temperature. Heat deflection temperature (HDT) is a measure of the short-term heat resistance of a material. The heat deflection temperature distinguishes between materials that are able to sustain light loads at high temperatures and those that lose their rigidity over a narrow temperature range. Thus, a high heat deflection temperature is indicative of a material whose modulus (i.e. Young's modulus) is high over a wide temperature range.
It is of interest, therefore, to increase the heat deflection temperature of polymeric materials without substantially affecting other desired properties of the material. Similarly, it is desired to increase the modulus of a material over a wide temperature range without substantially affecting other desired properties of the material.
Certain fillers have been added to polymer compositions in an attempt to increase heat deflection temperature. Fillers that have been added to polymer compositions include fibrous fillers with high modulus, such as fiberglass and carbon fiber, as well as non-fibrous fillers such as calcium carbonate, wollastonite, and mica. However, the addition of filler to a polymer will generally have a negative impact on other properties of the resulting polymer composition, such as ductility, impact strength, and toughness. Furthermore, it is a general rule that the more filler that is added, the greater its impact on the properties of the polymer composition.
Fillers with high aspect ratio have been investigated, because lesser amounts of these fillers are generally needed to produce a desired modulus-increasing effect for a given polymer composition. However, there are a number of problems resulting from the use of high-aspect-ratio fillers. It is typically more difficult to incorporate fillers with high aspect ratio into polymer. Often, the filler is not compatible with the polymer, and stable, highly-disperse mixtures of the filler in the polymer are difficult or impossible to achieve.
Macrocyclic polyester oligomer (macrocyclic oligoester, MPO) has unique properties that make it attractive as a matrix-forming resin for engineering thermoplastic composites. For example, MPO generally exhibits low melt viscosity and can polymerize at temperatures well below the melting point of the resulting polymer. An MPO of particular interest is macrocyclic poly(1,4-butylene terephthalate) oligomer.
It has been shown that mixtures of macrocyclic poly(1,4-butylene terephthalate) oligomer and organically-modified montmorillonite (a form of aluminosilicate) can be polymerized to produce a polymeric composition with high modulus (see, e.g. U.S. Pat. No. 5,707,439, by Takekoshi et al.). However, montmorillonite must be modified by cation exchange prior to incorporation with the MPO.